From the Oropesa Basin, one enters the Cuzco Basin through an opening in the sandstone cliffs of Angostura near the modern town of San Geronimo. On the slopes above the south bank of the Huatanay, just beyond Angostura, are the ruins of a score or more of gable-roofed houses of characteristic Inca construction. The ancient buildings have doors, windows, and niches in walls of small stones laid in clay, the lintels having been of wood, now decayed. When we asked the name of these ruins we were told that it was Saylla, although that is the name of a modern village three miles away, down the Huatanay, in the Oropesa Basin. Like Piquillacta, old Saylla has no water supply at present. It is not far from a stream called the Kkaira and could easily have been supplied with water by an azequia less than two miles in length brought along the 11,000 feet contour. It looks very much like the case of a village originally placed on the hills for the sake of comparative security and isolation and later abandoned through a desire to enjoy the advantages of living near the great highway in the bottom of the valley, after the Incas had established peace over the highlands. There may be another explanation. It appears from Mr. Cook's studies that the deforestation of the Cuzco Basin by the hand of man, and modern methods of tillage on unterraced slopes, have caused an unusual amount of erosion to occur. Landslides are frequent in the rainy season. Opposite Saylla is Mt. Picol, whose twin peaks are the most conspicuous feature on the north side of the basin. Waste material from its slopes is causing the rapid growth of a great gravel fan north of the village of San Geronimo. Professor Gregory noticed that the streams traversing the fan are even now engaged in burying ancient fields by "transporting gravel from the head of the fan to its lower margin," and that the lower end of the Cuzco Basin, where the Huatanay, hemmed in between the Angostura Narrows, cannot carry away the sediment as fast as it is brought down by its tributaries, is being choked up. If old Saylla represents a fortress set here to defend Cuzco against old Oropesa, it might very naturally have been abandoned when the rule of the Incas finally spread far over the Andes. On the other hand, it seems more likely that the people who built Saylla were farmers and that when the lower Cuzco Basin was filled up by aggradation, due to increased erosion, they abandoned this site for one nearer the arable lands. One may imagine the dismay with which the agricultural residents of these ancient houses saw their beautiful fields at the bottom of the hill, covered in a few days, or even hours, by enormous quantities of coarse gravel brought down from the steep slopes of Picol after some driving rainstorm. It may have been some such catastrophe that led them to take up their residence elsewhere. As a matter of fact we do not know when it was abandoned. Further investigation